Die and method of manufacturing cast product

ABSTRACT

According to one embodiment, a biscuit section, a product section in which a cast product is to be cast, and an overflow section which is provided on the opposite side of the biscuit section with respect to the product section are provided between a stationary die and a movable die of a die. The die includes a die surface provided with a concave section in which a rib of the cast product is to be cast. The concave section includes an inner peripheral surface of the concave section which includes a first surface spreading perpendicularly to a direction from the biscuit section toward the overflow section, and positioned on the overflow section side of the inner peripheral surface, and a second surface spreading in the direction from the biscuit section toward the overflow section. Surface roughness of the first surface is finer than surface roughness of the second surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2008-170172, filed Jun. 30, 2008, the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Field

One embodiment of the present invention relates to a technique associated with die casting.

2. Description of the Related Art

In die casting, when a cast product is removed from a die, die release resistance (so-called product die release resistance) acts on the product. If the die release resistance is large, the product cannot be removed from the die smoothly. For this reason, the die surface of the die is polished by using an abrasive or the like, and the surface roughness of the die surface is made small, thereby intending to reduce the die release resistance.

In Jpn. Pat. Appln. KOKAI Publication No. 3-5041, a die is disclosed in which the die release resistance of the movable die is made larger than that of the stationary die. In this die, the surface roughness of the movable die is made coarser than that of the stationary die. As a result of this, when the die is opened, the product is prevented from adhering to the stationary die.

Incidentally, when the product is removed from the die, the die release resistance does not act uniformly on the entire product, and relatively large die release resistance locally acts in some cases. If relatively large die release resistance acts locally, there is the possibility of the product being deformed when removed from the die. Such deformation of the product is an example of the defective casting.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A general architecture that implements the various feature of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention.

FIG. 1 is an exemplary perspective view showing a die according to a first embodiment of the present invention in a disassembled state;

FIG. 2 is an exemplary perspective view showing a cast product according to the first embodiment of the present invention;

FIG. 3 is an exemplary plan view showing an internal structure of the die according to the first embodiment of the present invention;

FIG. 4 is an exemplary perspective view schematically showing the concave sections of the die surface of the die shown in FIG. 3;

FIG. 5 is an exemplary cross-sectional view taken along line F5-F5 of the die shown in FIG. 4;

FIG. 6 is an exemplary cross-sectional view of the die shown in FIG. 5 in a state where the die is filled with molten metal;

FIG. 7 is an exemplary perspective view schematically showing a concave section of a die surface of a die according to a second embodiment of the present invention;

FIG. 8 is an exemplary perspective view schematically showing a concave section of a die surface of a die according to a third embodiment of the present invention; and

FIG. 9 is an exemplary perspective view schematically showing concave sections of a die surface of a die according to a fourth embodiment of the present invention.

DETAILED DESCRIPTION

Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment of the invention, a die for die casting according to the present invention comprises: a stationary die; and a movable die to be combined with the stationary die. In a state where the movable die is combined with the stationary die, (i) a biscuit section into which molten metal is to be injected, (ii) a product section in which a cast product is to be cast, and (iii) an overflow section which is provided on the opposite side of the biscuit section with respect to the product section are formed between the stationary die and the movable die. The die comprises a die surface provided with a concave section in which a rib of the cast product is to be cast. The concave section comprises an inner peripheral surface which comprises a first surface spreading perpendicularly to a direction from the biscuit section toward the overflow section, and positioned on the overflow section side of the inner peripheral surface, and a second surface spreading in the direction from the biscuit section toward the overflow section. Surface roughness of the first surface is finer than surface roughness of the second surface.

In general, according to one embodiment of the invention, a method of manufacturing a cast product by die casting according to the present invention comprises: preparing a die comprising a stationary die, and a movable die to be combined with the stationary die, wherein in a state where the movable die is combined with the stationary die, (i) a biscuit section into which molten metal is to be injected, (ii) a product section in which a cast product is to be cast, and (iii) an overflow section which is provided on the opposite side of the biscuit section with respect to the product section are provided between the stationary die and the movable die; combining the movable die with the stationary die; and injecting molten metal into the biscuit section. The die comprises a die surface provided with a concave section in which a rib of the cast product is to be cast. The concave section comprises an inner peripheral surface which comprises a first surface spreading perpendicularly to a direction from the biscuit section toward the overflow section, and positioned on the overflow section side of the inner peripheral surface, and a second surface spreading in the direction from the biscuit section toward overflow section. Surface roughness of the first surface is finer than surface roughness of the second surface.

Dies 1, and methods of manufacturing a cast product 2 according to embodiments of the present invention will be described below with reference to FIGS. 1 to 9.

FIG. 1 shows a die 1 according to a first embodiment of the present invention. The die 1 is used for die casting of, for example, the cold-chamber die casting system. For example, a magnesium alloy, aluminum alloy, or zinc ally is put into this die 1 as molten metal by pressure. It should be noted that the die according to the present invention is not limited to the above materials, and can be widely used for die casting in which various materials are used as molten metal.

FIG. 2 shows an example of a cast product 2 which is a product cast by using the die 1. The cast product 2 is, for example, a component constituting a part of a housing of an electronic apparatus such as a portable computer. It should be noted that the cast product to which the present invention can be applied is not limited to the above example, and various other products may be produced.

As shown in FIG. 2, the cast product 2 comprises a horizontal wall 3, and a vertical wall 4 rising from a peripheral edge part of the horizontal wall 3, thereby having a box-like shape opened on one side thereof. The cast product 2 has, for example, a rectangular shape. The cast product 2 comprises an exterior surface 2 a which become an outer front surface of an end product when the product 2 is incorporated in the end product, and a back surface 2 b which become an inner surface of the end product.

The cast product 2 comprises, for example, ribs 5 and 6 (hereinafter referred to as the first and second ribs 5 and 6) provided to rise from the back surface 2 b. The second rib 6 is an example of “another rib”. To the rib mentioned in the present invention, ribs formed for various purposes widely correspond. It should be noted that the number of ribs provided on the cast product 2 is not limited to two, and may be one, or three or more. Further, the rib mentioned in the present invention may be a rib provided on the exterior surface 2 a of the cast product 2. Furthermore, the size or the shape of the rib mentioned in the present invention is not limited to a specific size or shape.

As shown in FIG. 1, the die 1 comprises a stationary die 11, and a movable die 12 to be combined with the stationary die 11. Further, the movable die 12 is provided with eject pins 13 for removing the cast product 2 from the movable die 12.

The stationary die 11 is fixed to a stationary platen (not shown). The stationary die 11 comprises a stationary die plate 14, a cavity member 15, and an inlet member 16. The stationary die plate 14 is fixed to the stationary platen, and comprises a concave section (not shown) to which a cavity member 15 is attached on a surface opposed to the movable die 12. The cavity member 15 is attached to the concave section, and is opposed to the movable die 12. The cavity member 15 comprises a die surface 15 a (see FIG. 5) for forming, for example, the exterior surface 2 a of the cast product 2. The inlet member 16 is a cylindrical shaper and comprises a through-hole into which an injection plunger of the casting machine is inserted.

On the other hand, the movable die 12 comprises a movable die plate 17, a core member 18, and a dividing piece 19. The movable die 12 is fixed to a movable platen (not shown), and can be freely advanced or retreated between a die closed position in which the movable die 12 is combined with the stationary die 11, and a die opened position in which the movable die 12 is separated from the stationary die 11.

The movable die plate 17 is fixed to the movable platen, and comprises a concave section 17 a to which a core member 18 is attached on a surface opposed to the stationary die 11. The core member 18 is attached to the concave section 17 a, and is opposed to the stationary die 11. The core member 18 comprises a die surface 18 a for forming, for example, a back surface 2 b of the cast product 2.

In the state where the movable die 12 is combined with the stationary die 11 as shown in FIG. 3, an internal space 21 into which molten metal is to be pressed is formed between the stationary die 11 and the movable die 12. FIG. 3 schematically shows the internal space 21 for convenience of explanation. In FIG. 3, molten metal flows from above to below in the figure.

As shown in FIG. 3, the internal space 21 in the die 1 comprises a biscuit section 22, a product section 23, a fan gate 24, an overflow section 25, and a chillvent section 26.

The biscuit section 22 is provided inside the inlet member 16, and is a part which receives the high temperature molten metal from the injection apparatus of the casting machine at a high speed. That is, the biscuit section 22 is a section into which the molten metal is to be injected. The product section 23 is a space in which the cast product 2 is to be cast, and comprises a dug-down surface corresponding to a shape of the cast product 2.

The fan gate 24 is provided between the biscuit section 22 and the product section 23, and is a flow path for guiding the molten metal from the biscuit section 22 to the product section 23. The fan gate 24 comprises a runner 27 and a gate 28. The runner 27 is continuous with the biscuit section 22, and configured to guide the molten metal injected into the biscuit section 22 toward the product section 23.

The gate 28 is provided between the runner 27 and the product section 23. The thickness of the gate 28 is reduced as compared with the runner 27. The thickness of the gate 28 is sharply reduced at a position thereof closer to the product section 23, whereby the flow speed of the molten metal is accelerated toward the product section 23.

The overflow section 25 and the chillvent section 26 are provided on the opposite side of the biscuit section 22 and the fan gate 24 with respect to the product section 23. The overflow section 25 receives air inside the product section 23 pushed out by the molten metal, and reduces the filling resistance of the molten metal in the product section 23. Further, a flow tip of the molten metal flows into the overflow section 25. As a result of this, deteriorated molten metal at the flow tip is pushed out to the outside of the product section 23. The chillvent section 26 is a part having a function of a barrage for preventing the deteriorated molten metal from running out of the die 1.

In the die 1 as described above, the molten metal flows from the biscuit section 22 toward the overflow section 25. In this description, the term “flow direction (or current direction) of molten metal” Is defined as a direction from the biscuit section 22 toward the overflow section 25. It should be noted that thick arrows in FIGS. 3 to 9 indicate the flow direction M of the molten metal.

Next, the die surface 18 a of the die 1 will be described below in detail.

As shown in FIG. 3, the die 1 comprises first and second concave sections 31 and 32. The first concave section 31 is a concavity in which the first rib 5 of the cast product 2 is to be cast. The second concave section 32 is a concavity in which the second rib 6 of the cast product 2 is to be cast. In the die 1 according to this embodiment, the first and second concave sections 31 and 32 are provided on, for example, the die surface 18 a of the movable die 12 (see FIG. 5).

More specifically, the product section 23 is formed between the die surface 15 a of the stationary die 11, and the die surface 15 a of the movable die 12. The die surface 15 a of the stationary die 11 comprises a main surface 33 facing a region 23 a (so-called main section 23 a of the product section 23) in which the horizontal wall 3 of the cast product 2 is to be cast. The die surface 18 a of the movable die 12 comprises a main surface 34 facing the main region 23 a. Although FIG. 5 shows the first concave section 31 as a representative, the first and second concave sections 31 and 32 are sunk, for example, upwardly from the main surface 34 of the movable die 12. The first and second concave sections 31 and 32 are connected to the main region 23 a at the edges 35 and 36 of the concave sections 31 and 32.

FIG. 4 schematically shows inner peripheral surfaces 40 and 50 of the concave sections 31 and 32 extracted from the die 1. As shown in FIGS. 3 and 4, each of the first and second concave sections 31 and 32 is formed into a shape of, for example, a rectangular parallelepiped.

The first concave section 31 comprises an inner peripheral surface 40. The inner peripheral surface 40 of the first concave section 31 comprises a first surface 41, second surfaces 42 and 43, and a third surface 44. The first surface 41 spreads perpendicularly to the direction from the biscuit section 22 toward the overflow section 25 (i.e., the flow direction M of the molten metal), and is positioned on the overflow section 25 side (i.e., the downstream side in the flow direction M of the molten metal) of the inner peripheral surface 40. The second surfaces 42 and 43 spread in the direction from the biscuit section 22 toward the overflow section 25 (i.e., the flow direction M of the molten metal). The third surface 44 spreads perpendicularly to the direction from the biscuit section 22 toward the overflow section 25 (i.e., the flow direction M of the molten metal), and is positioned on the biscuit section 22 side (i.e., the upstream side in the flow direction M of the molten metal) of the inner peripheral surface 40.

Likewise, the second concave section 32 comprises an inner peripheral surface 50. The inner peripheral surface 50 of the second concave section 32 comprises a first surface 51, second surfaces 52 and 53, and a third surface 54. The first surface 51 spreads perpendicularly to the direction from the biscuit section 22 toward the overflow section 25 (i.e., the flow direction M of the molten metal), and is positioned on the overflow section 25 side (i.e., the downstream side in the flow direction M of the molten metal) of the inner peripheral surface 50. The second surfaces 52 and 53 spread in the direction from the biscuit section 22 toward the overflow section 25 (i.e., the flow direction M of the molten metal). The third surface 54 spreads perpendicularly to the direction from the biscuit section 22 toward the overflow section 25 (i.e., the flow direction M of the molten metal), and is positioned on the biscuit section 22 side (i.e., the upstream side in the flow direction M of the molten metal) of the inner peripheral surface 50.

Here, the surface roughness of the first surface 41 of the first concave section 31 is finer than that of the second and third surfaces 42, 43, and 44 of the first concave section 31. Further, the surface roughness of the first surface 51 of the second concave section 32 is finer than that of the second and third surfaces 52, 53, and 54 of the second concave section 32.

An example of the surface roughness of the first surfaces 41 and 51 of the first and second concave sections 31 and 32 is, for example, surface roughness obtained by polishing the surface by means of an abrasive having a grain size of No. 3000 to No. 6000. On the other hand, an example of the surface roughness of the second and third surfaces 42, 43, 44, 52, 53, and 54 of the first and second concave sections 31 and 32 is, for example, surface roughness obtained by polishing the surface by means of an abrasive having a grain size of No. 1000 to No. 2000. It should be noted that the grain size number in this description is based on Japanese Industrial Standards (JIS).

The die 1 as described above is manufactured, for example, in accordance with the following procedures. First, all the first to third surfaces 41, 42, 43, 44, 51, 52, 53, and 54 are polished up to the surface roughness of the second and third surfaces 42, 43, 44, 52, 53, and 54. Thereafter, the first surfaces 41 and 51 are polished by using an abrasive having a finer grain size.

Next, an example of a method of manufacturing a cast product 2 using the die 1 will be described below.

First, the above-mentioned die 1 is prepared, and the die 1 is set on the casting machine. Further, a raw material (for example, a magnesium alloy) is melted into molten metal. Then, the casting cycle is started. First, the movable die 12 is moved to be combined with the stationary die 11, and the die 1 is clamped.

Subsequently, molten metal is injected into a sleeve coupled to the inlet member 16, the injection plunger is forced out at a high speed, and the molten metal is pressed into the biscuit section 22 of the die 1.

When the solidification of the cast product 2 is advanced to a certain degree, the movable die 32 moves to open the die. At this time, the cast product 2 is released from the stationary die 11 to remain held in the movable die 12. After that, the cast product 2 is removed from the movable die 12 by using the eject pins 13. As a result of this, one cycle of the die casting is completed.

Next, the function of the die 1 will be described below.

As shown in FIG. 3, the molten metal injected into the biscuit section 22 flows from the biscuit section 22 toward the overflow section 25 through the main section 23 a of the product section 23. Further, as shown in FIG. 5, a part of the molten metal flowing through the main section 23 a of the product section 23 flows into the first and second concave sections 31 and 32.

According to the die 1 associated with this embodiment, the surface roughness of the first surfaces 41 and 51 is made finer than that of the second and third surfaces 42, 43, 44, 52, 53, and 54. Thus, relatively large die release resistance hardly acts from the first surfaces 41 and 51. As a result of this, it is possible to smoothly remove the cast product 2 from the movable die 12.

According to the die 1 and the method of manufacturing the cast product 2 having the configurations described above, it is possible to reduce defective casting.

The present inventors have found that in the die casting in which molten metal is injected into the die by relatively large force, the cast product 2 is liable to stick easier to the first surfaces 41 and 51 than to the second and third surfaces 42, 43, 44, 52, 53, and 54.

That is, the first surfaces 41 and 51 are positioned on the downstream side of the flow of the molten metal, and hence the molten metal directly collides against the first surfaces 41 and 51 at a large flow speed unlike in the case of the second and third surfaces 42, 43, 44, 52, 53, and 54. It can be considered that force directed to the first surfaces 41 and 51 acts on the molten metal, whereby the ribs 4 and 6 of the cast product 2 are made liable to easily stick to the first surfaces 41 and 51.

It has been found by the present inventors that, when the cast product 2 is removed from the die 1, the die release resistance acting between the first surfaces 41 and 51 and the ribs 5 and 6 is liable to have a larger value than the die release resistance acting between the second and third surfaces 42, 43, 44, 52, 53, and 54 and the ribs 5 and 6, and a large load (die release resistance) is liable to act locally on the cast product 2. Such local and large die release resistance is liable to become a cause of defective casting particularly in a cast product having a small fundamental thickness.

Thus, in the die 1 according to this embodiment, the surface roughness of the first surfaces 41 and 51 spreading perpendicularly to the flow direction M of the molten metal, and positioned on the downstream side in the flow direction M of the molten metal is made finer than that of the second surfaces 42, 43, 52, and 53 spreading in the flow direction M of the molten metal. This enables equalization of the die release resistance acting from the first surfaces 41 and Sir and the die release resistance acting from the second surfaces 42, 43, 52, and 53, and improves the balance of the die release resistance acting on the entire ribs 5 and 6. That is, it becomes possible to make large die release resistance hardly act locally on the ribs 5 and 6. As a result of this, it becomes possible to, when the cast product 2 is removed from the die 1, make the cast product 2 be hardly deformed, and realize reduction in the occurrence of defective casting of the cast product 2.

In order to smoothly remove a cast product from the die, it is conceivable that deformation of the cast product can be prevented by making surface roughness of all the shape elements of the die surfaces small, and by making the die release resistance small. However, in this case, a large number of man-hours is required to polish all the shape elements of the die surfaces.

On the other hand, in the die 1 according to this embodiment, polishing of the surfaces of the concave sections 31 and 32 is nicely varied, thereby equalizing the die release resistance acting on the surfaces of the ribs 5 and 6. Thus, the cast product 2 is prevented from being deformed when the cast product 2 is removed from the die by balancing the die release resistance. That is, in the die 1 according to this embodiment, it is possible to manufacture a die 1 capable of realizing reduction in defective casting by a relatively small number of man-hours.

It should be noted that making the surface roughness of the first surfaces 41, 51 finer than that of the second and third surfaces 42, 43, 44, 52, 53, and 54 may be realized by polishing up the first surfaces 41 and 51 or by making the surface roughness of the second and third surfaces 42, 43, 44, 52, 53, and 54 lower than before.

Next, a die 1i and a method of manufacturing a cast product 2 according to a second embodiment of the present invention will be described below with reference to FIG. 7. It should be noted that a configuration having a function identical with or similar to the configuration of the first embodiment will be denoted by the same reference symbol, and a description thereof will be omitted.

FIG. 7 schematically shows inner peripheral surfaces 64 and 70 of a concave section 31 extracted from a die 1. As shown in FIG. 7, the concave section 31 comprises a first section 61, and a second section 62 formed deeper than the first section 61. That is, the depth H of the second section 62 from the main surface 34 is larger than the depth h of the first section 61 from the main surface 34. In other words, the concave section 31 has a shape in which a first concave section having a depth H, and a second concave section having a depth h are joined to each other.

The first section 61 comprises an inner peripheral surface 64. The inner peripheral surface 64 of the first section 61 comprises a first surface 65, and second surfaces 66 and 67. The first surface 65 is a downstream side surface of the first section 61. The first surface spreads perpendicularly to a direction from a biscuit section 22 to an overflow section 25 (i.e., a flow direction M of molten metal), and is positioned on the overflow section 25 side (i.e., the downstream side in the flow direction M of the molten metal) of the inner peripheral surface 64. The second surfaces 66 and 67 spread in the direction from the biscuit section 22 toward the overflow section 25 (i.e., the flow direction M of the molten metal).

The second section 62 comprises an inner peripheral surface 70. The inner peripheral surface 70 of the second section 62 comprises a first surface 71, second surfaces 72 and 73, and a third surface 74. The first surface 71 is a downstream side surface of the second section 62. The first surface 71 spreads perpendicularly to the direction from the biscuit section 22 toward the overflow section 25 (i.e., the flow direction M of the molten metal), and is positioned on the overflow section 25 side (i.e., the downstream side in the flow direction M of the molten metal) of the inner peripheral surface 70. The second surfaces 72 and 73 spread in the direction from the biscuit section 22 toward the overflow section 25 (i.e., the flow direction M of the molten metal). The third surface 74 spreads perpendicularly to the direction from the biscuit section 22 toward the overflow section 25 (i.e., the flow direction M of the molten metal), and is positioned on the biscuit section 22 side (i.e., the upstream side in the flow direction M of the molten metal) of the inner peripheral surface 70.

Here, the surface roughness of the inner peripheral surface 70 is finer than that of the inner peripheral surface 64 of the first section 61. As a specific example, the surface roughness of the first surface 71 of the second section 62 is finer than that of the first surface 65 of the first section 61. Further, the surface roughness of the first surface 65 of the first section 61 is finer than that of the second and third surfaces 66, 67, 72, 73, and 74 of the first and second sections 61 and 62.

An example of the surface roughness of the first surface 71 of the second section 62 is, for example, surface roughness obtained by polishing the surface by means of an abrasive having a grain size of No. 3000 to No. 6000. An example of the surface roughness of the first surface 65 of the first section 61 is, for example, surface roughness obtained by polishing the surface by means of an abrasive having a grain size of No. 1000 to No. 2000. An example of the surface roughness of the second and third surfaces 66, 67, 72, 73, and 74 of the first and second sections 61 and 62 is, for example, surface roughness obtained by polishing the surface by means of an abrasive having a grain size of No. 800 to No. 1000. The remaining configurations of the die 1, and the method of manufacturing the cast product 2 other than those that have been described above are the same as those of the first embodiment.

According to the die 1 and the method of manufacturing the cast product 2 having the configurations described above, it is possible to reduce defective casting. That is, the die release resistance of the second section 62 the depth of which is relatively large in the concave section 31 is larger than that of the first section 61 the depth of which is relatively small by an amount corresponding to H-h, and hence there is the possibility of relatively large die release resistance locally acting when the cast product 2 is removed from the die 1.

However, in the die 1 according to this embodiment, the surface roughness of the inner peripheral surface 70 of the second section 62 is made finer than that of the inner peripheral surface 64 of the first section 61. By virtue of this, equalization of both the die release resistance acting from the second section 62, and the die release resistance acting from the first section 61 is enabled, and it becomes hard for large die release resistance to locally act on the rib 5 of the cast product 2. As a result of this, the cast product 2 becomes hard to be deformed when removed from the die 1, and reduction in defective casting of the cast product 2 can be realized.

Further, when the surface roughness of the first surface 71 of the second section 62 is made finer than that of the first surface 65 of the first section 61, the die release resistance acting from the second section 62, and the die release resistance acting from the first section 61 can be further equalized, and reduction in defective casting of the cast product 2 can be further promoted.

Next, a die 1, and a method of manufacturing a cast product 2 according to a third embodiment of the present invention will be described below with reference to FIG. 8. It should be noted that a configuration having a function identical with or similar to the configuration of the first and second embodiments will be denoted by the same reference symbol, and a description thereof will be omitted.

FIG. 8 schematically shows inner peripheral surfaces 64, 70, and 81 of a concave section 31 extracted from a die 1. As shown in FIG. 8, the concave section 31 comprises first to third sections 61, 62, and 81. A depth H1 of the second section 62 is larger than a depth h of the first section 61. A depth H2 of the third section 81 is larger than the depth H1 of the second section 62.

The surface roughness of an inner peripheral surface 70 of the second section 62 is finer than that of an inner peripheral surface 64 of the first section 61. Further, the surface roughness of an inner peripheral surface 82 of the third section 81 is finer than that of the inner peripheral surface 70 of the second section 62. The remaining configurations of the die 1, and the method of manufacturing the cast product 2 other than those that have been described above are the same as those of the second embodiment.

According to the die 1 and the method of manufacturing the cast product 2 having the configurations described above, it is possible to reduce defective casting as in the second embodiment.

Next, a die 1, and a method of manufacturing a cast product 2 according to a fourth embodiment of the present invention will be described below with reference to FIG. 9. It should be noted that a configuration having a function identical with or similar to the configuration of the first embodiment will be denoted by the same reference symbol, and a description thereof will be omitted.

FIG. 9 schematically shows inner peripheral surfaces 40 and 50 of concave sections 31 and 32 extracted from a die 1. As shown in FIG. 9, the die surface 18 a comprises first and second concave sections 31 and 32. In the second concave section 32 according to this embodiment, a depth thereof from the main surface 34 is larger than that of the first concave section 31. That is, the second concave section 32 is formed deeper than the first concave section 32. The first and second concave sections 31 and 32 are independent of each other, and are provided, for example, close to each other.

An inner peripheral surface 40 of the first concave section 31 comprises a first surface 41 (ire., a downstream side surface), second surfaces 42 and 43, and a third surface 44. Likewise, an inner peripheral surface 50 of the second concave section 32 comprises a first surface 51 (i.e., a downstream side surface), second surfaces 52 and 53, and a third surface 54.

Here, the surface roughness of the inner peripheral surface 50 of the second concave section 32 is finer than that of the inner peripheral surface 40 of the first concave section 31. As a specific example, the surface roughness of the first surface 51 of the second concave section 32 is finer than that of the first surface 41 of the first concave section 31. Further, the surface roughness of the first surface 41 of the first concave section 31 is finer than that of the second and third surfaces 42, 43, 44, 52, 53, and 54 of the first and second concave sections 31 and 32. The remaining configurations of the die 1, and the method of manufacturing the cast product 2 other than those that have been described above are the same as those of the first embodiment.

According to the die 1 and the method of manufacturing the cast product 2 having the configurations described above, it is possible to reduce defective casting. That is, in the second concave section 32 having a relatively large depth, the die release resistance is larger than in the first concave section 31 having a relatively small depth, and there is the possibility of relatively large die release resistance acting locally when the cast product is removed from the die.

However, in the die 1 according to this embodiment, the surface roughness of the inner peripheral surface 50 of the second concave section 32 is made finer than that of the inner peripheral surface 40 of the first concave section 31. By virtue of this, equalization of both the die release resistance acting from the second concave section 32, and the die release resistance acting from the first concave section 31 is enabled, and it becomes hard for large die release resistance to locally act on the cast product 2. As a result of this, the cast product 2 becomes hard to be deformed when removed from the die 1, and reduction in defective casting of the cast product 2 can be realized.

Further, when the surface roughness of the first surface 51 of the second concave section 32 having a relatively large depth is made finer than that of the first surface 41 of the first concave section 31, the die release resistance acting from the second concave section 32, and the die release resistance acting from the first concave section 31 can be further equalized, and reduction in defective casting of the cast product 2 can be further promoted.

The die 1, and the method of casting the cast product 2 according to each of the first to fourth embodiments of the present invention have been described above. However, the present invention is not limited to these. The constituent elements of the present invention can be modified and embodied in the implementation stage within the scope not deviating from the gist of the invention.

While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 

1. A die for die casting comprising: a stationary die; and a movable die to be combined with the stationary die, wherein in a state where the movable die is combined with the stationary die, (i) a biscuit section into which molten metal is to be injected, (ii) a product section in which a cast product is to be cast, and (iii) an overflow section which is provided on the opposite side of the biscuit section with respect to the product section are provided between the stationary die and the movable die, the die comprises a die surface provided with a concave section in which a rib of the cast product is to be cast, the concave section comprises an inner peripheral surface which comprises a first surface spreading perpendicularly to a direction from the biscuit section toward the overflow section, and positioned on the overflow section side of the inner peripheral surface, and a second surface spreading in the direction from the biscuit section toward the overflow section, and surface roughness of the first surface is finer than surface roughness of the second surface.
 2. The die of claim 1, wherein the inner peripheral surface of the concave section comprises a third surface spreading perpendicularly to the direction from the biscuit section toward the overflow section, and positioned on the biscuit section side of the inner peripheral surfacer and the surface roughness of the first surface is finer than surface roughness of the third surface.
 3. The die of claim 1, wherein the concave section comprises a first section, and a second section formed deeper than the first section, the second section comprises an inner peripheral surface which comprises a downstream side surface spreading perpendicularly to the direction from the is biscuit section toward the overflow section, and positioned on the overflow section side of the inner peripheral surface of the second section, the first section comprises an inner peripheral surface which comprises a downstream side surface spreading perpendicularly to the direction from the biscuit section toward the overflow section, and positioned on the overflow section side of the inner peripheral surface of the first section, and surface roughness of the downstream side surface of the second section is finer than surface roughness of the downstream side surface of the first section.
 4. The die of claim 1, wherein the die surface is provided with a second concave section in which a second rib of the cast product is to be cast, the second concave section is formed deeper than the first concave section, the second concave section comprises an inner peripheral surface which comprises a downstream side surface spreading perpendicularly to the direction from the biscuit section toward the overflow section, and positioned on the overflow section side of the inner peripheral surface of the second concave section, the first concave section comprises an inner peripheral surface which comprises a downstream side surface spreading perpendicularly to the direction from the biscuit section toward the overflow section, and positioned on the overflow section side of the inner peripheral surface of the first concave section, and surface roughness of the downstream side surface of the second concave section is finer than surface roughness of the downstream side surface of the first concave section.
 5. The die of claim 1, wherein the concave section comprises a first section, and a second section formed deeper than the first section, the first section and the second section each comprise an inner peripheral surface, and surface roughness of the inner peripheral surface of the second section is finer than surface roughness of the inner peripheral surface of the first section.
 6. The die of claim 1, wherein the die surface is provided with a second concave section in which a second rib of the cast product is to be cast, the second concave section is formed deeper than the first concave section, the first concave section and the second concave section each comprise an inner peripheral surface, and surface roughness of the inner peripheral surface of the second concave section is finer than surface roughness of the inner peripheral surface of the first concave section.
 7. A die for die casting comprising: a stationary die; and a movable die to be combined with the stationary die, wherein in a state where the movable die is combined with the stationary die, (i) a biscuit section into which molten metal is to be injected, (ii) a product section in which a cast product is to be cast, and (iii) an overflow section which is provided on the opposite side of the biscuit section with respect to the product section are provided between the stationary die and the movable die, the die comprises a die surface provided with a concave section in which a rib of the cast product is to be cast, the concave section comprises a first section, and a second section formed deeper than the first section, the first section and the second section each comprise an inner peripheral surface, and surface roughness of the inner peripheral surface of the second section is finer than surface roughness of the inner peripheral surface of the first section.
 8. A method of manufacturing a cast product by die casting comprising: preparing a die comprising a stationary die, and a movable die to be combined with the stationary die, wherein in a state where the movable die is combined with the stationary die, (i) a biscuit section into which molten metal is to be injected, (ii) a product section in which a cast product is to be cast, and (iii) an overflow section which is provided on the opposite side of the biscuit section with respect to the product section are provided between the stationary die and the movable die, the die comprising a die surface provided with a concave section in which a rib of the cast product is to be cast, the concave section comprising an inner peripheral surface which comprises a first surface spreading perpendicularly to a direction from the biscuit section toward the overflow section, and positioned on the overflow section side of the inner peripheral surface, and a second surface spreading in the direction from the biscuit section toward the overflow section, and surface roughness of the first surface being finer than surface roughness of the second surface; combining the movable die with the stationary die; and injecting molten metal into the biscuit section. 